Automatic grinding machine

ABSTRACT

This invention relates to an automatic grinding machine and, more particularly, to apparatus for generating surfaces of revolution by use of the abrasive process, wherein the operation of the machine is under closed loop force control.

United States Patent Hahn et al.

[ 51 Oct. 3, 1972 1 51/139 X .51/165.93 .5l/l65.93

[ AUTOMATIC GRINDING MACHINE 3,415,017 12/1968 Murray..................;. 72 Inventors; Robert S. Hahn, Northbom; 2,612,008 9/1952 Kumholm..............

Ri p Lindsay, Marlboro bmh 3,197,921 8/1965 H0hler.........

f Mass. 2,649,646 8/1953 Remmer...... 3,404,490 10/1968 Estabrook [73] Assignee: The Heald Machine Company, Wor- 2,924,913 2/1960 cester, Mass.

Primary Examinerl-lar0ld D. Whitehead [22] Ffled' May 1970 Attorney-Norman S. Blodgett [2]] App]. No.: 39,619

ABSTRACT This invention relates to an automatic grinding machine and, more particularly, to apparatus for generating surfaces of revolution by use of the abrasive process, wherein the operation of the machine is under closed loop force control.

1A 59 M /b 14 9 52 References Cited UNITED STATES PATENTS 3 Claims, 6 Drawing figures 3,274,738 9/1966 Kuniholrn Ill 65 PATENTEDIIBI 3 1972 SHEET 1 BF 4 RICHARD P. LINDSAY INVENTORS.

XK IL w m S T W O R TABLE MOTION FIG 2 PATENTEflncI 3 m2 sum 2 0r 4 ADJUST ROUGH FORCE LEVEL ADJUST {0N EASE 0N ADJUST FINISH FORCE LEVEL FORCE ADJUST SYSTEM FIG. 3'

FIG. 6

AUTOMATIC GRINDING MACHINE BACKGROUND OF THE INVENTION In the art of grinding and, particularly, that of internal grinding (where the abrasive wheel is mounted on a cantilevered spindle) attempts have been made in the past to make the operation completely automatic. In this way, the human factor would be removed from the process and the time-consuming adjustments necessary for adequate grinding would be removed. Internal and external production grinding machines are generally set up to produce workpieces of a certain level of quality with regard to surface finish, size, taper, and thermal damage for reasonably short-cycle times. At the present time, considerable knowledge and experience on the part of the setup man or operator is required to set up and adjust grinding machines to accomplish this purpose. It is desirable for several reasons to relieve the operator or the setup man of the many thought-requiring procedures which he must use to set up the machine and to keep it producing. The field of automatic control offers the means for accomplishing this by providing better control of the grinding process and simpler operating procedures. In the past, however, complete control which takes into consideration all the grinding parameters, has been difficult, if not impossible.

In internal grinding, the wheelhead spindle, when loaded against the workpiece, undergoes a radial deflection and an angular deflection. The angular deflection causes taper, if it is not compensated for, and the radial deflection causes changes in bore size. The presence of these elastic effects complicates the operation and the setup of internal grinders. Therefore, if for some reason the operator desires to increase the grinding force, increased spindle deflection results. This, in turn, will require a readjustment of the size contacts as well as a readjustment of the wheelhead or wheelhead swivel to compensate for the increased deflection. In other words, the taper in the hole and the final contact positions are both functions of the grinding force. It would be desirable if the grinding force did not cause size or finish stock changes or taper changes. If this were true, internal grinders would be greatly simplified operationally. The unskilled workman would not have to concern himself about spindle deflections nor for readjustment for both size and taper after changing the grinding force. Moreover, the grinding force could then be changed as the wheel wore smaller, thereby maintaining the proper cutting action and surface finish for new wheels as well as old worn out wheels. Other reasons for wanting to change the grinding force during a grinding cycle are to compensate for wheel dulling and/or variations in workpiece grindability.

It would be desirable also to predict the amount of wheel wear at any given time in accordance with the force-time history which the wheel has undergone during the grinding cycle, the wheel wear taking place under these circumstances according to a fairly welldefined law. If this were known, it would be possible to adjust the amount of compensation before dress.

Another parameter for which it would be desirable to compensate is the dullness of the grinding wheel. This dullness results from flats wearing on each abrasive grain and from picking up new grains, so that both the real area of contact and the effective grain spacing increases; slow cutting and thermal damage to the workpiece may result. At the same time, variations in workpiece grindability cause slow grinding and surface finish variations from piece to piece.

The initial runout in the unfinished workpieces which are presented to the grinding machine may vary from part to part. At present, the machine cycle has to be set to accommodate the worst runout; that is, the roughing force must be built up gradually, otherwise, the wheel will break down during rounding up. If the cycle is set to accommodate the piece having the worst runout (which may occur once in 500 pieces), all other workpieces could be ground in less time, so that, cycle time is sacrificed on the true-running pieces. Considerable time may be saved by having the machine sense the runout and adapt the rate of built-up of roughing force accordingly.

At the end of the grinding cycle, it has been common practice to use a sparkout between rough (or first) size and final size. This procedure consists in grinding by means of the residual deflection in the wheel spindle. However, the difficulty is that this is an uncontrolled part of the grinding cycle; that is to say, the feed and the forces involved are allowed to vary in ac cordance with the deflection of the spindle without any control. It would be desirable to have the machine control this cycle, so that a definite pattern of forces between the wheel and the workpiece would be used.

Another problem that exists is that of chatter. Wheel regenerative chatter is one of several types of grinding chatter which occurs in external and internal cylindrical grinders. It is the most prevalent type. In this type of chatter, mechanical roughness in the machine or small variations of wheel hardness cause small variations of the force existing between wheel and work. This causes the coupled system (wheelhead, spindle, wheel, workpiece, machine) to execute small oscillations at one of the system natural frequencies. This, in turn, causes further force pulsations to occur between wheel and workpiece, these pulsations being at the natural frequency. As a result, the grinding wheel wears more rapidly in certain places around its circumference than in others. This, then, aggravates the condition and a chatter gradually builds up as the wheel continues to grind. These and other difficulties experienced with the prior art devices have been obviated in a novel manner by the present invention.

It is, therefore, an outstanding object of the invention to provide an automatic grinding machine which gives a fine control of the force between the wheel and the workpiece in accordance with several important grinding parameters.

Another object of this invention is the provision of an automatic grinding machine in which the force between the wheel and the workpiece is varied during the rounding up portion of the cycle in accordance with the runout of the particular piece being ground.

A further object of the present invention is the provision of an automatic grinding machine which adjusts the force between the wheel and the workpiece in accordance with wheel dullness or workpiece hardness.

It is another object of the instant invention to provide an automatic grinding machine which regulates the force between the wheel and the workpiece during a sparkout portion of the cycle in accordance with a predetermined function.

A still further object of the invention is the provision of an automatic grinding machine in which the force between the wheel and the workpiece is modulated when chatter appears in order to suppress the chatter.

It is a further object of the invention to provide an automatic grinding machine in which the change of instantaneous force causes an adjustment of the wheelhead to maintain wheel deflection and final size contact position the same, irrespective of the force used.

It is a still further object of the present invention to provide an automatic grinding machine specially designed to make use of automatic control techniques for controlling force between the wheel and the workpiece in accordance with a number of measured grinding parameters.

With these and other objects in view, as will be apparent to those skilled in the art, the invention resides in the combination of parts set forth in the specification and covered by the claims appended hereto.

SUMMARY OF THE INVENTION In general, the invention consists of an automatic grinding machine having a workpiece support and an abrasive wheel support. A sensor is provided for measuring the instantaneous force between the wheel and the workpiece, and this sensor indicates this value of the instantaneous force to a control. The control operates on a feed means for producing the force between the workpiece and the wheel and serves to regulate it in accordance with various grinding parameters.

BRIEF DESCRIPTION OF THE DRAWINGS The character of the invention, however, may be best understood by reference to one of its structural forms, as illustrated by the accompanying drawings, in which:

FIG. 1 is a perspective view of an automatic grinding machine embodying the principles of the present invention,

FIG. 2 is a schematic plan view of the machine,

FIG. 3 is an electrical schematic of a force-adjusting system forming part of the invention,

FIG. 4 is a schematic diagram of a hydraulic force application system with a measuring and feedback system forming part of the invention,

FIG. 5 is a block diagram of a mechanical force and swivel application system, and

FIG. 6 is another schematic view of the apparatus.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring first to FIG. 1, wherein are best shown the general features of the invention, the automatic grinding machine, indicated generally by the reference numetal 10, is shown as consisting of a base 11 on which is mounted a wheelhead feed table 12. Suitable ways (not shown) extend between the base 11 and the table 12 and provide for motion transversely of a workpiece axis, which direction is generally indicated by the direction X on the diagram. A main feed cylinder 13 extends between the base 11 and the table 12 to bring about transverse feeding motion of the abrasive wheel 14 and the workpiece 15 (see FIG. 2). Mounted on the upper flat surface of the table 12 is a wheelhead swivel table 16 which is supported on the table by means of hydrostatic pads 17, 18, and 19, so that the table 16 is freely supported on a film of oil. A vertical pivot post 21 is mounted in the table 12 and extends upwardly into the pivot table 17 which is provided with two hydrostatic bearings 22 and 23. Extending upwardly from the top of the table 12 is an abutment 24 which is connected to the table 16 by a coil spring 25. Also extending between the abutment 24 and the table 16 is a diaphragm-type hydraulic actuator 26. Mounted on the top of the table 16 is a wheelhead 27 carrying in suitable bearings a spindle 28 at the outboard end of which is carried the abrasive wheel 14. A motor 29 is mounted on the table 16 and connected to the spindle 28 by a belt 31. Inherent in the apparatus are certain spring constants which are indicated on the diagram for the purpose of the discussion to follow. Among these are the spring constant K, associated with the actuator 26, the spring constant K, of the hydrostatic bearings 22 and 23 associated with the connection of the table 16 to the pivot post 21, and the spring constant K, of the longitudinal connection between the table 16 and the table 12.

Referring to FIG. 2, it can be seen that the table 16 is pivotal about the pivot post 21 at an angle indicated generally by the angle 0. The workpiece 15 is supported in a manner not shown in the usual way on the base 12 by means of a workhead which supports the workpiece and rotates it about the axis of the surface of revolution to be generated.

FIG. 1 also shows the presence of transducers 32 and 33 which receive the pressure in the pivot post bearings 22 and 23, respectively, and generate an electrical signal proportional to the pressure in these bearings. Since the center of pressure between the wheel 14 and the workpiece 15 is located above the pivot post, the force is indicated to these bearings as a difference, which difference is indicative of the instantaneous force.

Referring next to FIG. 3, it can be seen that the electrical control system is provided with a source 34 of DC. electricity which is connected on one side to ground and on the other side to a line 35, the other end of which is connected to a potentiometer 36. The other side of the potentiometer is connected to ground, while the mid-point connection is connected to one end of another potentiometer 37. The other side of this potentiometer is connected by a line 38 through a normallyopen contactor 39.

The line 35 is also connected to one end of a potentiometer 41 whose movable arm is connected to one end of another potentiometer 42 which is connected through a normally-open contactor 43 to one side of a normally-closed contactor 44. The other sides of the two contactors 39 and 44 are connected by a line 45 to one side of a normally-closed contactor 46, the other side of which is connected through a l0 megohm resistor 47 to ground. The other side of the contactors 39 and 44 are also connected to one side of a normallyopen contactor 48 which is connected to a line 49. A point between the contactor 44, on the one hand, and the contactor 48, on the other hand, is connected through a capacitor 49a to ground. A point in the line 49 on the other side of the contactor 48 is connected through a normally-closed contactor 51 and through a 47 megohm resistor 52 to ground. The output of this force-adjusting system, as shown in FIG. 3, is on the line 49 and presents a selected voltage which, in turn, determines the force during rough grind and the force during finish grind, depending upon the opening and closing of the various contactors.

In general, the controls, valves, cylinders, and like apparatus associated with the grinding machine are similar to that shown in the Patent of Hohler No. 3,197,921. The particular controls specifically shown in this application are those by which the present machine varies from the Hohler patent controls.

The voltage arriving in the line 49 enters the hydraulic force application system shown in FIG. 4, goes through a summing junction station 53, the other side of which is attached by a line 54 to a valve 55. This is a pressure regulating valve which receives 500 psi fluid pressure and a pressure appears on an output conduit 56 with a value determined by the value of the voltage impressed on the valve by the line 54. A gage 57 gives a reading of the voltage following the valve. The line 56 is connected to an input port of a solenoid valve 58 which is connected to an output line 59 for finish force pressure or an output line 61 for rough grinding force pressure. The line 59 contains a pressure divider 68. The pressure following the solenoid 58 and the lines 59 and 61 come together at an inlet conduit 62, the line 59 having a check valve 63 following the hydraulic resistance 68. The conduit 62 is connected to the inlet port of a solenoid 64 whose output line 65 also contains a pressure-indicating gage 66. A gage 67 resides in the line 62 to indicate the pressure at that point. The line 65 is connected to the hydraulic resistance 168, the output of which is connected to a line 69 leading to the actuator 26. The line 65 is also connected to a line 71 leading to the cross slide cylinder 13. A line 72 containing a check valve 73 is connected between the lines 69 and 71. The line 71 is also connected to an input valve of a solenoid valve 74, the output line of which is connected through a throttle 75 to sump 76. A check valve 77 is connected around the throttle 75.

A line 78 representing the pressure difference across hydrostatic pockets 22 and 23 enters the system shown in FIG. 4 and is connected to one side of the transducers 32 and 33, and an output line 79 from the transducers is connected to the voltage mixer station 53. An intermediate point in the line 79 is connected to ground through a meter 81. This meter includes a relay which closes when a signal from the transducers indicates that pressure is on the wheel. This means the wheel has contacted the workpiece and the relay starts the charging of capacitor 49a and the built-up of force for the rough grind. It also serves to turn on the flow divider 68 in order to provide for finish grind.

FIG. 5 is a block diagram of the mechanical force and swivel application system. The input on the line 69 is indicative of the hydraulic pressure serving the actuator 26 to bring about swiveling of the table about the pivot post 21. The other line 71 introduces into the system a pressure particularly selected for use in the cross-slide piston 13. The result on the system is to produce an angle indicated by the line 82 and also the grinding force at the line 83 which acts on the spindle 28.

Leaving the block diagram of FIG. is a line 78 lead ing to the voltage-mixing station 53 which is a feedback line adjusting the forces as necessary to comply with the commanded value entering on line 49, FIG. 3.

The block diagram in FIG. 5 represents the vibrational and dynamic properties of the hydraulicmechanical system shown in FIG. 1 and is used to analyze dynamic behavior. The grinding force acting on the wheel is represented by line69 which produces a torque on the swivel plate 16, the dynamics of which is represented by block 97. The pulsating component of the grinding force during the rounding up of the workpiece is represented as a disturbance w(t) which applies an additional pulsating torque to the swivel plate (junction 85) as well as a pulsating force (junction 87). The grinding force also acts on the main cross-slide 21 and is represented by line 71.

The operation of the apparatus will now be readily understood in view of the above description. When the grinding wheel 14 is in the bore of the workpiece 15 and a force is exerted between the two, the grinding wheel spindle 28 bends. The amount of bending is proportional to the force exerted and is inversely propor' tional to the stiffness of the spindle. Thus, when the force changes, the deflection and angle of deflection both change. These changes affect the resultant size (when cross-slide table contacts are used for sizing), and taper is produced in the workpiece. To eliminate these fluctuations, the present invention provides a hydrostatic swivel plate 16 which rests on the crossslide table 12. The actuator 26 receives a percentage of the grinding force pressure, and this causes the actuator to expand, thus pushing against the swivel plate which causes the swivel plate to rotate an angular amount (angle 0) about the pivot post 21, as shown in FIG. 2. Then, when the wheel enters the hole and the force is applied between the wheel and the workpiece, the angular deflection of the spindle will cancel the initial cocking angle 0, causing the wheel surface to be straight or parallel to the longitudinal motion between the wheel and the workpiece provided by the-conventional table grinding machine facilities. Thus, as the grinding force is varied, the pressure to the actuator 26 is varied and so is the cocking angle 0, creating a forceinsensitive taper control system. The pivot post 21 is fastened to the cross-slide table 12 and contains the four hydrostatic bearings 22, 23, etc. Since the pressure in the pockets of these bearings is sensitive to the forces that the bearing must support, a sensing of the bearing pressure is a sensing of the applied grinding force. With the transducers 32 and 33 connected to the pockets in the X-direction, a measure of the difference between the pressures in the rear and front pockets is a measure of the grinding force applied to the system. The electrical system is designed to send a command signal (the shape of which may be varied) to a servo valve, the output of which is a fluid pressure. This output pressure is applied to the cross-slide piston 13 to produce a grinding force F,,. The signals from the bearing-pocket transducers 32 and 33 are used as a feedback signal and are compared to the command signal to assure the desired force.

Damage of a thermal nature is produced in the work by dull wheels. A measure of dulling is the real area of contact worn onto the grinding wheel grits (wear by attrition). An indirect measure of the real area is obtained by measuring Q,,, the ratio of the plunge grinding velocity E, to the instantaneous force F since a relation exists between the real area of contact and the ability of the wheel to remove stock. Such measurements can result in control of thermal damage due to grinding, which damage is an important parameter in grinding high-temperature alloys. A feedback loop is proposed to control grinding damage.

The behavior of the grinding system (including the machine) may be described by a set of four equations. The machine is shown schematically in FIG. 6 with the parameters indicated. The equations are derived using the following relationships:

K spring constant of the system in pounds/inch x the angular spring constant of the system in inch pounds/radian n .r/ t v/ l /K) AD/2 shift in work center line due to variation of CD. when work is located against shoe 601. In this manner, it is possible to derive a Position Equation, a Metal Removal Law Equation, a Wheel Wear Law Equation, and a Machine Equation.

The Position Equation gives the instantaneous workpiece radius X(t) in terms of the cross slide displacement z(t), the wheel radius y(t), the angular and lateral machine deflections l and (r and the OD. size variation AD/2 (where grinding on shoes). This appears as:

The second equation is the Metal Removal Law. To begin with, one may take a linear differential equation expressed as:

where 0,, is the slope of the plunge velocity curve vs. force intensity b width of wheel-work contact F, normal grinding force The radial velocity of stock removal 7,, is propor tional to force intensity F lb. If desired, one may consider non-linear laws as well, but this will not be done for the purposes of the present invention.

The third equation is the Wheelwear Law. Here, a power series of F and a power of t, the grinding time, have been chosen, based on experimental data as a realistic representation describing wheel wear. The constants (1,, B, and a can be determined experimentally. The wheel wear is given by the following equation:

where u y,,y the radial Wheelwear. Q, B, and a are empirical constants.

The fourth equation for controlled force grinding machines as in FIG. 6 is:

da; du F1-FC Neglecting the cross slide mass and rounding up dynamics is reasonable in the low frequency range and serves as a simplified starting point for the development of an automatic control system.

With respect to the control for size and taper, an idea of the magnitude of the taper errors and deflection errors that can occur in internal grinding have been obtained experimentally with two popular size wheelheads. It has been shown that a 10 pound force change will cause a little over 0.0001 inch change in deflection (0.0002 inch in diameter change) and about 0.0002 inch per inch taper change.

The present invention shows the control system for making the bore size and the taper independent of the grinding force. A position transducer, for instance, or LVDT 119 is provided between the base 11 and the cross slide 12. Also mounted on the cross slide is the dynamometer consisting of the transducers 32 and 33 which determine the actual grinding force at the wheel. A signal proportional to the actual grinding force is compared with a reference signal and the error is fed to an electro-hydraulic valve which, in turn, supplies pressure to the feed cylinder of the cross slide, thereby producing the desired grinding force at the wheel. The input voltage at a summing junction is compared with the force signal from the dynamometer to produce an error signal to the amplifier and pressure regulating valve which, in turn, acts on the cross slide to generate the desired force. The input voltage at the summing junction is also fed to another junction where a closed loop on the wheelhead swivel plate maintains the proper angle 0 to nullify exactly the angular deflection of the wheel. In this way, taper errors due to changes in grinding force are eliminated.

The input to the first summing junction representing the desired grinding force is also applied (after multiplication by the proper gain) to another junction where it compensates for the cross slide position signal for both lateral and angular positional errors according to the Position Equation. In this way, control of grinding by means of cross slide switch contacts are made invariant with respect to force; that is to say, the size points determined by the dresser diamond as a reference do not change as the grinding force varies. In short, the force loop and the angle loop and the deflection correction eliminate all size and taper variations due to force changes. This permits the force to be varied at will without causing size or taper variations.

The wheel wear predicator estimates the wheel wear in accordance with the force profile (force-time history which the wheel has undergone during the grinding cycle) and the Wheelwear Law. The dynamometer signal is fed to the gain A ,/b which produces the instantaneous rate of wheel wear du/dt. This quantity is integrated to give the running wheel wear u(t). This, is turn, is applied to a junction to adjust the cross slide contacts size points for wheel wear. In abrasive machining operations, where large quantities of stock are removed, the amount of wheel wear during roughing may be significant and this control will hold size in spite of wheel wear. The running wheel wear u(t) is also added to the set-in value of desired depth of dress at a junction. This automatically sets the required amount of compensation to give the proper depth of dress; thus, the compensation for new large wheels or small used wheels will vary. It also will vary in accordance with the amount of rough stock. With this control, when properly set, it is not necessary for the operator to cut and try to find the correct compensation (which will be set for the worst case large stock and small wheel). It can be seen that diamond life and the number of pieces per wheel are improved. The compensation is integrated to give the accumulated compensation. This signal is used to vary the wheel wear parameter A, and also to reduce to reduce the force on the wheel as the wheel becomes smaller (wheel size modulation). This is accomplished at another junction. In this way, the surface finish and cutting rate of the small used wheel can be maintained at the proper values. This will permit the wheel to be used down to a smaller diameter and thus give more parts per wheel change.

One of the methods of measuring wheel dullness that is used in connection with the present invention is the metal removal parameter method. The output force signal F from the transducers is divided by the width of contact to give the force intensity f The stock removal rate X is obtained as the difference between the cross slide velocity 2 and the wheel wear rate it. The metal removal parameter A is formed by dividing X by f,. This is compared with a set in value of metal removal parameter A at a junction. The difference or error in A multiplied by a gain K is applied to another junction to cause an increase in force to occur whenever a slowcutting workpiece or a dull wheel are present. This tends to put greater forces on hard-to-grind workpieces or dull wheels. The degree of dullness can be used to call for a dress or to signal an alarm that thermal damage may be occurring. The dullness control tends to keep the cycle time constant in spite of workpiece grindability variations. The surface finish will also be more uniform.

The rounding up control operates by controlling the rate of build-up of force, so that the peak instantaneous force on the wheel does not exceed a certain limit. The output signal P, of the transducers is separated into a quasi-steady component e and an alternating component e the sum of which is formed at a junction and then applied at another junction. Thus, if the dynamometer senses a large runout, the value of e will be large. A small error signal will occur at the lastnamed junction and the quasi-steady force build-up will be slow. For true running workpieces, the component e will be small and the force signal will be built up rapidly, thereby producing a very fast cycle.

It is obvious that minor changes may be made in the form and construction of the invention without departing from the material spirit thereof. It is not, however, desired to confine the invention to the exact form herein shown and described, but it is desired to include all such as properly come within the scope claimed.

The invention having been thus described, what is claimed as new and desired to secure by Letters Patent 1s:

1. An automatic grinding machine, comprising a. a workpiece support,

b. an abrasive wheel support, including a cantilevered spindle adapted to carry an abrasive wheel at one end, said spindle being rotatably mounted at its other end in a wheelhead, said wheelhead being mounted on a table which is mounted for pivotal movement about a vertical axis, said table being biased by springs to a neutral position of pivoting and a hydraulic cylinder provided to produce pivoting a ay from the neutralposition, c. a sensor or measuring the instantaneous force between the wheel and the workpiece,

. a control for receiving a signal from the sensor indicative of the instantaneous force, wherein said control transmits to the cylinder a regulating pressure proportional to the said instantaneous force between the wheel and workpiece, so that pivoting of the table takes place in an amount exactly compensating for deflection of the wheel spindle due to the said instantaneous force.

e. feed means for producing this force between the workpiece and the wheel and receiving a regulating signal from the control; and

f. a size means indicating to the said control when a predetermined finish size is reached, the control regulating the feed means so that the force between the wheel and the workpiece is reduced as a definite predetermined function of the remaining stock before final size and maintaining the position of the wheel at a predetermined angle to the workpiece axis by changing the angle of the wheelhead in response to changes in force.

2. An automatic grinding machine as recited in claim 1, wherein the control senses long-range changes in stock removal rate due to workpiece or wheel dullness and regulates the feed means to increase the force between the wheel and workpiece to bring the stock removal rate up to a predetermined amount.

3. An automatic grinding machine as recited in claim 1, wherein the said control variations in force between the wheel and the workpiece indicative ofdullness on a portion only of the wheel circumference associated with chatter and regulates the feed means to produce a modulation of the force between the wheel and the workpiece, thereby modulating the natural frequency to suppress the chatter.

' l III 

1. An automatic grinding machine, comprising a. a workpiece support, b. an abrasive wheel support, including a cantilevered spindle adapted to carry an abrasive wheel at one end, said spindle being rotatably mounted at its other end in a wheelhead, said wheelhead being mounted on a table which is mounted for pivotal movement about a vertical axis, said table being biased by springs to a neutral position of pivoting and a hydraulic cylinder provided to produce pivoting away from the neutral position, c. a sensor for measuring the instantaneous force between the wheel and the workpiece, d. a control for receiving a signal from the sensor indicative of the instantaneous force, wherein said control transmits to the cylinder a regulating pressure proportional to the said instantaneous force between the wheel and workpiece, so that pivoting of the table takes place in an amount exactly compensating for deflection of the wheel spindle due to the said instantaneous force. e. feed means for producing this force between the workpiece and the wheel and receiving a regulating signal from the control; and f. a size means indicating to the said control when a predetermined finish size is reached, the control regulating the feed means so that the force between the wheel and the workpiece is reduced as a definite predetermined function of the remaining stock before final size and maintaining the position of the wheel at a predetermined angle to the workpiece axis by changing the angle of the wheelhead in response to changes in force.
 2. An automatic grinding machine as recited in claim 1, wherein the control senses long-range changes in stock removal rate due to workpiece or wheel dullness and regulates the feed means to increase the force between the wheel and workpiece to bring the stock removal rate up to a predetermined amount.
 3. An automatic grinding machine as recited in claim 1, wherein the said control variations in force between the wheel and the workpiece indicative of dullness on a portion only of the wheel circumference associated with chatter and regulates the feed means to produce a modulation of the force between the wheel and the workpiece, thereby modulating the natural frequency to suppress the chatter. 